The present invention relates to apparatus for erecting arcuate walls of concrete or the like. More particularly, the invention relates to improvements in apparatus (also called slip forms) which can be used for erection of cylindrical, hemispherical or otherwise curved walls made of poured concrete or other suitable hardenable building material. Still more particularly, the invention relates to improvements in apparatus or forms of the type wherein a deformable (flexible) sheathing is secured to spaced-apart supports and its configuration can be changed by changing the angular position(s) of one or more supports.
It is already known to reinforce or stabilize an apparatus of the above outlined character by employing a composite girder including rigid (i.e., non-flexible) variable-length links which are articulately connected to each other in order to allow for a change in the configuration of the sheathing, and which also serve to hold the sheathing against deformation when the apparatus is in actual use. In many instances, the sheathing is made of wood panels but it is also known to assemble the sheathing of sheets which are made of steel or another metallic material. In many instances, especially in connection with the erection of cylindrical towers, chimneys and the like, the apparatus comprises two deformable sheaths, namely an outer sheath having a concave wallcontacting surface and an inner sheath having a convex wall contacting surface. The two sheaths are spaced apart from each other to define a space which is ready for reception of concrete or another hardenable building material. It is preferred to erect the apparatus in such a way that the space between the two sheaths is not traversed by cables, rods, anchor pins or other rigid or flexible parts which are embedded in the building material. The inserts not only weaken a concrete wall but also provide paths for the leakage of fluid which is especially undesirable if the erected structure is to constitute a water tower or another type of edifice for storage of liquids and/or other flowable materials. In such constructions, all solid inserts must be removed from the finished wall and the thus obtained holes must be sealed in a time-consuming operation. Another drawback of apparatus wherein the inner and outer sheaths are secured to each other by anchor pins or the like is that the anchor pins normally extend through the sheathings and are secured to the supports for the sheathings. This means that the supports for the outer sheathing must be properly aligned with the supports for the inner sheathing which is a time-consuming operation and contributes to the cost of the structure which is being erected.
An apparatus of the just described character is disclosed, for example, in German Pat. No. 21 40 638. In the patented apparatus, the supports for the inner sheathing (namely the sheathing which has a convex or at least partially convex surface in contact with the wall) are connected to each other by links each of which includes several straight sections. Such sections of each link are articulately connected to each other so that their mutual inclination can be changed before the thus oriented sections are fixed against further angular movement relative to each other. Pairs of neighboring supports are rigidly affixed to a section each of the adjacent links, and the mutual angular positions of such pairs of supports can be changed by means of bolts and nuts. Lock nuts are provided to fix the supports of the respective pair in selected positions.
The just described apparatus exhibits numerous additional drawbacks. The length of the links cannot be changed at will, i.e., the number of different link lengths is limited. This reduces the versatility of the patented apparatus because the apparatus cannot cause its sheathing to form a cylinder having any desired diameter. Attempts to overcome this drawback include the provision of an additional or extra section of variable length which is attached to one end of the apparatus. The extra section can be misplaced or the workmen may forget to bring it to the site of erection of a wall or the like so that the absence of the extra section can cause lengthy delays in assembly of the apparatus.
Another drawback of the patented apparatus is that the supports invariably extend at right angles to the rigid sections. Consequently, they cannot be oriented radially of the structure which is to be erected and this prevents the erection of a truly cylindrical structure. Attempts to overcome such drawback involve the utilization of auxiliary equipment which contributes to the initial and maintenance cost and prolongs the intervals which are required for erection or dismantling of the apparatus.
Still another drawback of the patented apparatus is that a change of setup takes up inordinately long intervals of time. For example, conversion of the apparatus into one that is used for the erection of larger- or smaller-diameter cylindrical towers or chimneys is very time consuming. Each such change necessitates an adjustment of the connection between each pair of supports for the sheathing and the respective rigid section of a link.
German Utility Model No. 77 04 885 discloses an apparatus which can be used as a slip form and has means for reinforcing a cylindrical sheathing. The reinforcing means employs links of infinitely variable length. Each link is a rod-like member and the end portions of neighboring links are connected to each other by pivot pins. Wedges are used to fix the neighboring links in selected angular positions relative to each other.
A drawback of the apparatus which is disclosed in the Utility Model is that it does not exhibit sufficient stability, i.e., the aforementioned wedges are not capable of standing the stresses which are likely to arise during pouring of a cylindrical wall of concrete or the like so that the mutual inclination of the links changes and the shape of the erected wall deviates from an optimum or desired shape. Moreover, the operators cannot adequately control the extent to which a wedge is driven between two neighboring links, and this also contributes to lack of stability and proneness to deformation when the apparatus is in actual use. Even if an inspection leads the person in charge to conclude that a wedge is in proper engagement with the respective links, the force with which the links are held against changes of their mutual angular positions depends solely on friction between the wedge and the links. Attempts to use wedges with roughened or toothed surfaces and/or to provide the adjacent portions of the links with roughened or toothed surfaces (i.e. to shift from a force-locking to a form-locking connection between a wedge and the neighboring links) have failed because this limits the versatility of the apparatus in that the links cannot be moved to an infinite number of angular positions. Moreover, the wedges are located at or very close to the pivot axes or bolts which connect the respective links to one another. This subjects the wedges to very pronounced deforming and other stresses. Therefore, the apparatus must employ oversized wedges or wedges consisting of extremely hard and highly expensive material. This apparatus also employs pairwise arranged supports which are parallel to each other and are connected to a common section of a variable-length link with the aforediscussed drawbacks.